In recent years, the field of electric motors has witnessed exponential growth in the use of BLDC brushless motors, due to the many advantages they offer, including the fact that these motors are smaller in size while delivering the same torque, they consume less electricity, have higher speeds, require less maintenance, dissipate heat better and can be overloaded.

One of the most critical issues with this type of SPM (Surface permanent magnets) motor is the complexity of attaching the magnets to the rotor, since they cannot be welded to it because at high temperatures permanent magnets suffer an irreversible loss of magnetic flux.


To overcome this problem Politubes, in conjunction with DuPont, has developed a special spiral-wound tube made of heat-shrinkable polyester (Mylar HS), which enables automated fixing of permanent magnets, thereby reducing the cost of assembling these motors.

The spiral-wound tube is fitted onto the rotor with the magnets in position and is then instantly heat-shrunk, resulting in a firm attachment of the magnets to the rotor, protection for the magnets from scratches, abrasions and polluting agents and no danger of cracking or damage to the delicate permanent magnets during the assembly process.

The temperatures used for heat-shrinking are well below the Curie point, and therefore three is no risk of reducing the magnetic flux of the magnets.

Other important advantages offered by the heat-shrinkable tubes include:

  1. Unlike very expensive steel rings, the spiral-wound tube also wraps around and protects the ends of the magnets, which are also subject to corrosion and which, if chipped, can cause the motor to seize.
  2. The trimming that often has to be done during the assembly process when using rigid rings is avoided; the Politubes spiral-wound tube adheres perfectly to the magnets, taking their shape and protecting them from cracking and scratching; this also guarantees perfect balancing of the rotor.
  3. Part of the assembly process is removed, since potentially costly and often manual bandage with tape impregnated with epoxy resisns can be eliminated; this avoids as well lenghty resin activation time in oven; productivity is thereby increased and hidden production costs reduced.
  4. The tubes can also be used successfully in combination with the epoxy glues used to fix the magnets, guaranteeing additional protection against the potential failure of the glue and detachment of the magnets, and against scratches or other polluting agents.
  5. The minimum dimensions are between 0.12 and 0.2 mm; this avoids any reduction in the magnetic flux of the rotor, and allows the magnets to achieve maximum performance.

In motors that use annular magnets produced by the compression molding of Nd-Fe-B Neodymium Iron Boron magnets with the addition of thermosetting resins (plastoferrite), our tube also protects the magnet from corrosion, given the fragility of the alloys used, thereby preventing the motor from seizing. The heat-shrinkable polyester tube is used at temperatures with peaks of up to 155°C.

The adhesives used, which have been carefully selected over forty years of experience, comply with all REACH and RoHS standards and ensure that the films used fully retain their original properties.

The Politubes R&D center remains at your disposal should you require anything, and to work together to design tailored, innovative solutions.

Download the DuPont-Politubes Case History